The plasma protein osmotic pressure (pi-c) is important because it opposes edema formation in the lung. The effectiveness of pi-c in opposing edema depends on the pulmonary capillary membrane osmotic reflection coefficient to protein. Reflection coefficient estimates made from dog lung lymph protein concentration data have been significantly lower than estimates made from studies of the effect of the effect of pi-c on capillary filtration rate. The objective for this project is to reconcile the difference. The first specific aim is to use a modified technique to estimate the reflection coefficient from lung lymph-data. The experiments will involve the collection of lung lymph in dogs with reduced pi-c. The second specific aim is to estimate the reflection coefficient from the effect of pi-c on fluid filtration in the lungs of anesthetized dogs. This will involve weighing the lungs. The capillary filtration rate will be estimated from the lung weight change and the reflection coefficient will be estimated from the capillary pressures necessary to cause equal filtration rates at control pi-c and with reduced pi-c. The third specific aim is to compare the osmotic reflection coefficient, estimated from the lymph protein data and the reflection coefficient estimated from the effect of pi-c on fluid filtration. The results of this project should lead to a better understanding of the role of plasma protein osmotic pressure in opposing lung edema.